1. Field of the Invention
The invention relates to a method for repair soldering of multi-pole miniature plug connectors on printed circuit boards, having signal contact pins in the SMT design and shroud pins in the THR design.
2. The Prior Art
Female multi-point connectors, as an example of multi-pole miniature plug connectors having signal contact pins in the SMT design and shroud pins in the THR design, consist essentially of a greater number of signal conductor tracks that are embedded in plastic chambers of contact disks, which carry shrouds on the outside, to improve the high-frequency properties of the female multi-point connectors (see, for example, German Patent No. DE 100 51 819 A1). The conductor tracks of the signal contacts are configured, at one end, as lyre-shaped spring contacts for blade-like counter-contacts, guided in their chambers in 90° arcs, and are provided with solder pins for being soldered to a circuit board at the other end. Several contact disks in turn are pushed into a plastic quiver, parallel to one another, and thereby joined together as a compact body. The shrouds also carry solder pins, which proceed in a comb-tooth-like manner from a sheet-metal edge of the shrouds, and are also soldered to the printed circuit board.
Female multi-point connectors are particularly used for connections between a printed circuit board of a module and a rear wall printed circuit board equipped with male multi-point connectors. Usually, the solder pins consist of base metal, such as a copper alloy, corresponding to the material of the signal conductor tracks, and are very small in their dimensions. For example, they have a width of 0.35 mm. The diameters of the metallized solder holes in the printed circuit boards are correspondingly small. The distances between the solder pins, or the solder holes, respectively, relative to one another are very close. They possess a grid dimension of 2.0 mm, for example. Therefore, only very small amounts of solder are allowed to be used when soldering the solder pins onto a printed circuit board. On the other hand, the mechanical connection and the electric current carrying capacity suffer if the solder contact between the solder pins and the solder holes is too slight, resulting in functional failures and shortening of the useful lifetime.
Often, the signal contact pins are configured as SMD pins (Surface Mounted Device) for surface mounting (SMT, Surface Mounting Technology), while the shield pins are contacted through according to the Through Hole Reflow (THR) technology.
In the SMT technology, solder paste deposits are applied to a printed circuit board by means of stencil or screen printing, in the grid dimensions of the solder pins. For soldering, the SMD pins are pressed onto a solder paste deposit with their little feet, in each instance. The melting process itself then takes place by means of temperature effect in a solder oven, whereby the SMD pins are mechanically and electrically connected with the solder paste deposits. A prerequisite for a good connection is that all of the solder pins rest against solder paste deposits that are applied to be as level, uniform, and precise in their position as possible, on a printed circuit board that is also as level as possible, at the slight pressure that is necessary for SMT soldering, and with as much of their area as possible. On the other hand, it is a benefit of SMT technology that no holes have to be made in the printed circuit board, and that the tolerance width with regard to the deviations in position of the solder pins relative to one another does not have to be kept extremely small transverse to the set-down direction of the components.
In the case of contacting according to the TH technology (Through-Hole Technology), the solder pins are inserted through small holes in the printed circuit board. A metal layer on the underside of the printed circuit board, the solder eye, forms the solder side. During the actual soldering process, the printed circuit board is drawn downward over a wave of liquid solder, in the wave soldering method. Since the holes are hardly any larger than the diameter of the pins, the TH technology demands a rather precise alignment of the solder pins. Otherwise, it can happen that not all of the solder pins find their solder hole, thereby causing functional problems of the module.
In the case of the so-called THR technology (Through-Hole-Reflow Technology) that links the two aforementioned technologies, also known in the technical world as “Pin-in-Paste Method,” the printed circuit boards are provided with metallically through-contacted bores, whereby analogous to the SMT technology, solder paste deposits are applied to the bores, which are through-contacted here. During component application, the needle-like solder pins of the component to be mounted, for example the shroud pins of a female multi-point connector, push the solder paste of the solder paste deposits at least partially through the bore hole, without great press-in pressure, so that during the subsequent reflow soldering, soldering of the solder pin, in each instance, within the through-contacted bore takes place. The solder, which is liquid at working temperature, flows into the ring gap between the solder hole and the solder pin, supported by capillary forces. By means of the solder paste that melts in the through-contacted bore and at the top of the contact pin, a similar solder point as that known from traditional wave soldering is obtained. The mechanical ability to withstand stress that is required for plug connectors, with regard to plug-in forces, remains guaranteed. A great advantage of the THR technology can be seen in that it can easily be integrated into the SMT production process, in other words only an application method for applying the solder paste deposits has to be used, and soldering itself can take place in one and the same heating pass, e.g. in a soldering oven. As compared with the SMT technology, the THR technology furthermore has the advantage that aside from a comparatively firm mechanical seat on the printed circuit board, there is also comparatively good electrical stress resistance. The solder pin length should be coordinated with the thickness of the printed circuit board, as much as possible, in order to be able to assess the final quality of the solder point, on the basis of the formation of the solder cones and their circumference wetting.
The repair of equipped printed circuit boards regularly presents problems. If, for example, the lyre contact of a contact spring of the female multi-point connector bends or breaks off in subsequent use, the female multi-point connector must be unsoldered by hand, the printed circuit board has to be cleaned of solder residues and any flux agent residues, as well as dirt, and a new female multi-point connector must be soldered in by hand. Currently, one makes do in connection with adding new equipment in that the necessary solder paste deposits for the SMD or THR pins are placed in the grid dimensions while being viewed through a magnifying glass, by means of a stencil and doctor, or by hand. However, due to the extraordinary fineness of the solder connections of a female multi-point connector and the small distances between solder pins, this is extremely difficult and time-consuming, since it is necessary to adhere to required tolerances and to avoid smearing of the solder paste on the printed circuit board when lifting off the application stencil. In this connection, it must also be seen that the printed circuit board is already equipped with numerous other components, which make the repair work even more difficult.